I am doing a roughness case study, hence I can only employ near-wall boundary condition implying my y+ <= 1. Hence my 1st grid cell height near the wall is 4micro m. I hence also obtain about 15 points in the laminar sub layer.

But maximum roughness height Ks is 2mm. According to Fluent User Guide, the distance from the wall to the centroid of the wall-adjacent cell should be greater than Ks, implying my first cell height should be 4mm!

If i increase y+ and make my first cell height 4mm, I neither get 10points within the laminar sublayer nor can i use near-wall modeling. I get about 2 points within the turbulent boundary layer!

What should I base my cell height on?

Thanks in advance, Johnson.Mendonca

Hi,

I may base it on Re-turbulent number.

All the best

If first cell height is less than roughness height Ks, how to mesh it ?